A reasonable, and admittedly naïve, attempt at an automated Rails + CircleCI + Heroku deploy script. 🐉 THERE BE DRAGONS! 🐲

heroku_deploy.sh

#!/usr/bin/env bash
#
# Usage: bin/heroku_deploy <heroku-app-name> [git-treeish : default=HEAD]

. ./shell_colors

set -euo pipefail

app_name=$1
app_remote=$app_name
deploy_treeish=${2:-HEAD}
deploy_sha=$(git rev-parse --verify $deploy_treeish)
use_maintenance_mode=1

# Do NOT put production into maintenance mode during deploys. We really need a better way of doing zero-downtime deploys.
# 🐉 THERE BE DRAGONS! 🐲
if [ "$app_name" = "<YOUR_PRODUCTION_HEROKU_APP_NAME_HERE>" ]; then
  use_maintenance_mode=0
fi

printf "☁️   Setting up heroku git remote '$app_remote'.\n"

# Unshallow the repo -- required for recent git upgrade on CircleCI
[[ ! -s "$(git rev-parse --git-dir)/shallow" ]] || git fetch --unshallow

if ! git remote | grep -q "$app_remote"; then
  git remote add "$app_remote" git@heroku.com:$app_name.git
fi
git fetch "$app_remote"

printf "\n🔐   Configuring ~/.netrc with Heroku credentials.\n"

if [[ ! -f ~/.netrc ]]; then
  touch ~/.netrc
  chmod 600 ~/.netrc # Heroku cli complains about permissions without this
fi

if grep 'api.heroku.com' ~/.netrc -q; then
  printf "\n⚠️${YELLOW}   You have existing credentials for 'api.heroku.com' and/or 'git.heroku.com'.${NO_COLOR}\n"
  printf "ℹ️   Ensure the credientals in '~/.netrc' are valid.\n"
else
  cat >>~/.netrc <<-EOF
machine api.heroku.com
  login $HEROKU_EMAIL
  password $HEROKU_TOKEN
machine git.heroku.com
  login $HEROKU_EMAIL
  password $HEROKU_TOKEN
EOF
fi

printf "\n💾   Checking for pending migrations and Heroku worker dyno size.\n"

migration_changes=$(git diff HEAD $app_remote/master --name-only -- db | wc -l)
prev_workers=$(heroku ps --app $app_name | { grep "^worker." || true; } | wc -l | tr -d ' ')

# migrations require downtime so enter maintenance mode
if [ $migration_changes -gt 0 ]; then
  printf "\n⚠️${YELLOW}   $migration_changes files needing migration.${NO_COLOR}\n"

  if [ "$use_maintenance_mode" -eq "1" ]; then
    heroku maintenance:on --app "$app_name"
  fi

  # Make sure workers are not running during a migration
  printf "\n⚠️${YELLOW}   Scaling $prev_workers down to '0'.${NO_COLOR}\n"
  heroku scale worker=0 --app "$app_name"
fi

printf "\n💾   Capturing DB backup for '$app_name'.\n"
heroku pg:backups capture --app "$app_name"

# deploy code changes (and implicitly restart the app and any running workers)
printf "\n⛅️   Pushing code to '$app_name'.\n"
git push "$app_remote" "$deploy_sha":refs/heads/master

# run database migrations if needed and restart background workers once finished
if [ $migration_changes -gt 0 ]; then
  printf "\n⏳   Migrating database for '$app_name'.\n"

  # ignore errors so failed db migrations don't immediately abort our deploy script.
  set +e
  heroku run bin/rake db:migrate --app "$app_name" --exit-code
  migration_status=$? # store the exit code
  set -e

  printf "\n👷   Scaling 'worker' dynos to '$prev_workers'.\n"
  heroku scale worker="$prev_workers" --app "$app_name"

  printf "\n♻️   Restarting dynos for '$app_name'.\n"
  heroku restart --app "$app_name"

  if [ "$use_maintenance_mode" -eq "1" ]; then
    heroku maintenance:off --app "$app_name"
  fi

  if test $migration_status -ne 0; then
    printf "💀${RED}   Migrations fails. Failing the build.${NO_COLOR}\n"
    exit $migration_status
  fi
fi

printf "\n🎉${GREEN}   Deploy for '$app_name' finished. Enjoy the new bits!${NO_COLOR}\n"

shell_colors.sh

#!/usr/bin/env bash

RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[0;33m'
NO_COLOR='\033[0m'
CLEAR_LINE='\r\033[K'